linux-kernel - Re: [patch 1/3] add the fsblock layer

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Message-ID: <18048.32372.40011.10896@notabene.brown>
Date:	Tue, 26 Jun 2007 12:48:20 +1000
From:	Neil Brown <neilb@...e.de>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [patch 1/3] add the fsblock layer

On Tuesday June 26, nickpiggin@...oo.com.au wrote:
> Chris Mason wrote:
> > 
> > The block device pagecache isn't special, and certainly isn't that much
> > code.  I would suggest keeping it buffer head specific and making a
> > second variant that does only fsblocks.  This is mostly to keep the
> > semantics of PagePrivate sane, lets not fuzz the line.
> 
> That would require a new inode and address_space for the fsblock
> type blockdev pagecache, wouldn't it? I just can't think of a
> better non-intrusive way of allowing a buffer_head filesystem and
> an fsblock filesystem to live on the same blkdev together.

I don't think they would ever try to.  Both filesystems would bd_claim
the blkdev, and only one would win.

The issue is more of a filesystem sharing a blockdev with the
block-special device (i.e. open("/dev/sda1"), read) isn't it?

If a filesystem wants to attach information to the blockdev pagecache
that is different to what blockdev want to attach, then I think "Yes"
- a new inode and address space is what it needs to create.

Then you get into consistency issues between the metadata and direct
blockdevice access.  Do we care about those?


NeilBrown
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